1. Field of the Invention
The present invention relates to a power supply control circuit whose electric power consumption can be decreased by cutting off the power supply to a controller in a stand-by state, and to a cooking device having the power supply control circuit.
2. Description of Related Art
FIG. 1, which is a circuit diagram of the first example of prior art, shows a power supply control circuit provided in a cooking device which has a door. In FIG. 1, a commercial AC power source 1 is connected with power lines 1a and 1b for supplying electric power to a load 6 of the cooking device. Used as the load 6 is, for example, a high-frequency generating circuit when the cooking device is a microwave oven, or a heater when the cooking device is a thermal heating oven.
Connected in series to the power line 1a are a filter coil 9a, a starting power supplying switch 3 and a power supply holding switch 4 constituted of a relay switch, which is controlled to be in an on-state in response to power supply to a controller 8 for use of the cooking device and controlled to be in an off-state when the cooking device is in a nonuse state. The starting power supplying switch 3 is connected to a terminal of the load 6. The starting power supplying switch 3, which is a door switch operating in response to the opening/closure of a door (not shown) of the cooking device, has a common terminal 3a connected to the power line 1a, a closure terminal 3b which is connected to the common terminal 3a when the door is in a closed state, and an opening terminal 3c which is connected to the common terminal 3a when the door is in an open state. The closure terminal 3b is connected to the load 6. The opening terminal 3c is connected to the AC power source 1 via an auxiliary power line 1c. 
Connected in series to the power line 1b are a filter coil 9b and a load exciting control relay switch 5 for controlling on/off of power supply from the AC power source 1 to the load 6. The load exciting control relay switch 5 is connected to the other terminal of the load 6.
Connected between the power lines 1a and 1b are a radio interference suppression capacitor 2 for suppressing radio interference and primary side terminals 7a and 7b of a stepdown transformer 7 which constitutes a control power supply unit. Moreover, radio interference suppression capacitors 12 and 13 (respectively having a capacity of 3,000 to 4,000 picofarad, for example) are respectively connected between the power line 1a and a grounded contact and between the power line 1b and the grounded contact.
Secondary side terminals 7c and 7d of the stepdown transformer 7 are connected via a rectification smoothing circuit (omitted in the figure) to a controller 8 which generates various kinds of control signals used for various kinds of control operations in the cooking device. A power supply holding control signal 4s outputted from the controller 8 controls the power supply holding switch 4 to be in an on-state. The power supply holding switch 4 is held in the on-state as long as the power supply holding control signal 4s is outputted. A load exciting control signal 5s outputted from the controller 8 controls on/off of a load exciting control relay switch 5.
The following description will explain the operations of the power supply control circuit. When the door is opened to place a material to be cooked in a cooking chamber for use of the cooking device, the common terminal 3a of the starting power supplying switch 3 constituted of a door switch is connected to the opening terminal 3c, and electric power is supplied from the AC power source 1 via the auxiliary power line 1c to the stepdown transformer 7. Upon the power supply to the stepdown transformer 7, the controller 8 is put into an operative state and outputs a power supply holding control signal 4s. The power supply holding control signal 4s turns on the power supply holding switch 4, and the power line 1a is connected to the AC power source 1 via the power supply holding switch 4. Since the power supply holding control signal 4s holds the power supply holding switch 4 in the on-state, power supply to the stepdown transformer 7 via the power lines 1a and 1b is maintained and thereby the controller 8 is kept in an operative state even when the door of the cooking device is closed again, the common terminal 3a of the starting power supplying switch 3 is connected to the closure terminal 3b again and power supply from the AC power source 1 via the opening terminal 3c is cut off.
Next, in response to an operator guidance through an operator control panel (not shown), the controller 8 outputs a load exciting control signal 5s. The load exciting control signal 5s turns on the load exciting control relay switch 5, electric power is supplied from the AC power source 1 to the load 6 via the power lines 1a and 1b, and a predetermined cooking operation is performed.
When the cooked material is taken out of the cooking chamber after the cooking operation finishes and it is judged that the cooking device is in a nonuse state (the judgment is performed based on, for example, whether opening/closure of the door is detected within a predetermined time after the detection of the opening/closure of the door at the end of the cooking operation), the output of the power supply holding control signal 4s stops, the power supply holding switch 4 is turned off, and thereby the electric power consumed while the controller 8 is in a stand-by state, i.e. since the controller 8 is put into a non-operative state until the cooking device is used next, is reduced.
FIG. 2, which is a circuit diagram of the second example of the prior art, shows a power supply control circuit provided in a cooking device which has a door. It should be noted that like codes are used to refer to like parts in this figure and FIG. 1, and detailed explanation thereof is omitted here. In FIG. 2, a door switch 31 is of a single junction type, and does not have the opening terminal 3c and the auxiliary power line 1c shown in FIG. 1. A push switch 11 as a starting power supplying switch is connected in parallel to the power supply holding switch 4. When the door of the cooking device is in a closed state, the door switch 31 is in an on-state, i.e., the terminal 31a connected to the power line 1a is connected with the terminal 31b connected to the load 6.
By pushing the push switch 11 for use of the cooking device, the push switch 11 is put into an on-state only while being pushed. When the push switch 11 is put into the on-state, the power line 1a is connected to the AC power source 1 and electric power is supplied to the stepdown transformer 7 via the power lines 1a and 1b. Upon the power supply to the stepdown transformer 7, the controller 8 is put into an operative state and outputs a power supply holding control signal 4s. The power supply holding control signal 4s turns on the power supply holding switch 4, and the power line 1a is connected to the AC power source 1 via the power supply holding switch 4.
The power supply holding control signal 4s holds the power supply holding switch 4 in the on-state even when the pushing operation against the push switch 11 is released and the push switch 11 is turned off. Consequently, power supply to the stepdown transformer 7 via the power lines 1a and 1b is maintained and the controller 8 is kept in the operative state.
FIG. 3, which is a circuit diagram of the third example of the prior art, shows a power supply control circuit provided in a cooking device which has a door. It should be noted that like codes are used to refer to like parts in this figure and FIGS. 1 and 2, and detailed explanation thereof is omitted here. In FIG. 3, the terminals of the power supply holding switch 4 are respectively connected to the common terminal 3a and the opening terminal 3c of the starting power supplying switch 3. The opening terminal 3c of the starting power supplying switch 3 is connected to the primary side terminal 7a of the stepdown transformer 7. In this circuit, since the radio interference suppression capacitor 2 is connected in parallel to the AC power source 1 (between the power lines 1a and 1b), it is necessary to keep the user, who pulls off a power source plug (not shown) to be connected to the AC power source 1, from receiving an electric shock by touching blades of the power source plug where voltage is generated due to the storage voltage generated by the charge in the radio interference suppression capacitor 2. For this purpose, a discharging resistor 10 is connected in parallel to the radio interference suppression capacitor 2. It is generally supposed to be necessary that the radio interference suppression capacitor 2 has a capacity of 0.1 microfarad or more in view of radio interference suppression. Connecting such a large capacitor to the AC power source 1, it is necessary to connect a discharging resistor 10 of approximately 1 megohm to meet Japanese safety standards, for example. When such a discharging resistor 10 is used, a total electric power consumption exceeds the negligible level even though the amount of the electric current in the stand-by state is minute.
When the door of the coking device is opened, the common terminal 3a of the starting power supplying switch 3 constituted of a door switch is connected to the opening terminal 3c, and electric power is supplied from the AC power source 1 via the power line 1a to the stepdown transformer 7. The further operations are the same as those of FIG. 1, and omitted here.
In the first example and the second example of the prior art, since the power supply holding switch is disposed in series to the power line, there arises a problem that it is necessary to employ a power supply holding switch (a relay switch) with a large current-carrying capacity which allows an electric current to flow, the electric current being as large as the load current which flows when the load is in an operative state.
In the third example of the prior art, in which a discharging resistor is connected in parallel to the radio interference suppression capacitor to discharge the charge in the radio interference suppression capacitor, there arises another problem that electric power consumption due to the discharging resistor is generated in the stand-by state though the amount of the power consumption is minute.
The present invention has been made with the aim of solving the above problems, and it is an object thereof to provide a power supply control circuit having a serial circuit of a power supply holding switch and a radio interference suppression capacitor which is connected between power lines, with which a rated current of the power supply holding switch requires a small capacity by precluding the load current from flowing to the power supply holding switch, and moreover, stand-by electric power consumption due to the discharging resistor for discharging charge in the radio interference suppression capacitor can be decreased.
A power supply control circuit according to the present invention comprises: a control power supply unit to which electric power is supplied from power lines via a starting power supplying switch; a controller, to which electric power is supplied from the control power supply unit, for controlling power supply from a power source to a load; and a power supply holding switch, which is controlled to be in an on-state in response to the power supply to the controller, for maintaining the power supply from the power lines to the control power supply unit until the power supply holding switch is controlled to be in an off-state. In the power supply control circuit, a serial circuit of the power supply holding switch and the radio interference suppression capacitor is connected between the power lines, the node of the power supply holding switch and the radio interference suppression capacitor is connected to the node of the starting power supplying switch and the control power supply unit, and thereby electric power is supplied to the control power supply unit via the power supply holding switch.
Another power supply control circuit according to the present invention comprises: a control power supply unit to which electric power is supplied from power lines via a starting power supplying switch; a controller, to which electric power is supplied from the control power supply unit, for controlling power supply from a power source to a load; and a power supply holding switch, which is turned on in response to the power supply from the control power supply unit, for maintaining the power supply from the power lines to the control power supply unit until the power supply holding switch is controlled to be in an off-state by the controller. In the power supply control circuit, a serial circuit of the power supply holding switch and the radio interference suppression capacitor is connected between the power lines, the node of the power supply holding switch and the radio interference suppression capacitor is connected to the node of the starting power supplying switch and the control power supply unit, and thereby electric power is supplied to the control power supply unit via the power supply holding switch.
The starting power supplying switch is a switch which is turned on manually or automatically, such as a push switch which is held in an on-state only while, or at the moment, the user pushes the switch, and a door switch or a closure switch which is turned on in response to an opening operation of a door or a closure.
Employable as the power supply holding switch is a semiconductor switch such as a relay switch and a TRIAC (a triode AC switch).
In the power supply control circuit according to the present invention which is constructed to reduce the electric power consumption by cutting off the power supply to the controller in a stand-by state, the rated current of the power supply holding switch (a relay switch) for controlling the power supply to the controller requires a small capacity, and moreover, the discharging resistor which is necessary for the prior art to discharge the charge in the radio interference suppression capacitor is unnecessary. The reduction of the electric power consumption due to the discharging resistor and the employment of the power supply holding switch with a small capacity allow costs to be decreased.
The cooking device according to the present invention having a high-frequency generating circuit comprises the power supply control circuit according to the present invention which uses the high-frequency generating circuit as the load.
The invention can provide a cooking device comprising the power supply control circuit in which the rated current of the power supply holding switch (a relay switch) requires a small capacity, and moreover, the discharging resistor of the radio interference suppression capacitor which is necessary for the prior art is unnecessary. Consequently, it is possible to realize a cooking device of low electric power consumption and small cost.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.